Accompanying the demands for smaller size and operational improvements in cell phones, portable computers, and other electronic devices, there has been a demand for higher integration levels and smaller semiconductor chips that are used in these electronic devices. The flip-chip assembly that connects a bare chip to a substrate is one technology used in the assembly of semiconductor chips with a high integration level and smaller pitch. In the flip-chip assembly, the bump electrodes formed on the principal surface of the integrated circuit of the semiconductor chip are directly connected opposite the electrodes or lands on the substrate. This flip-chip assembly method is replacing the method of connecting the electrodes on the semiconductor chip to the substrate by means of wire bonding.
The flip-chip assembly adopts the following methods: the method in which a bare chip on which bumps have been formed is pressed and bonded to a substrate on which an anisotropic conductive film has been laminated, and the method in which a bare chip on which solder bumps have been formed is mounted on a substrate, and connections are formed by reflow soldering. In the latter method of connection, in order to prevent breakage due to the concentration of stress on the solder bumps, an underfill resin is injected between the bare chip and the substrate so as to relieve the stress.
Patent Reference 1 pertains to a semiconductor device manufacturing method in which an underfill resin is injected. In this method, in order to solve the problem that when liquid underfill resin is injected from an end portion of the semiconductor chip, the resin will creep to the upper surface (a principal surface) of the semiconductor chip and will become attached to the upper surface, the upper surface of the semiconductor chip is subjected to plasma treatment after sealing the underfill resin. As a result, the heat sink can be easily connected to the upper surface of the semiconductor chip, so that the heat dissipation property is improved.
When the liquid underfill resin is injected into the space between the semiconductor chip and the substrate while the semiconductor chip and the substrate are in the flip-chip connection state, the underfill resin moves deep into this space due to capillary action to seal the solder bumps between the semiconductor chip and the substrate.
However, for certain reasons, the underfill resin cannot penetrate to the vicinity of the center of the semiconductor chip as it should, and air bubbles or other voids form in the resin. One reason concerns the effect of the physical size and shape of the semiconductor chip and substrate. For example, as the pitch of the electrodes of the semiconductor chip and the bumps becomes as small as 50 μm, or the number of the electrodes approaches 400, or the spacing between the semiconductor chip and the substrate becomes 15 μm or smaller, the propagation resistance of the resin increases, so that it is difficult for the resin to penetrate deeply, and voids are formed. As numerous voids form in the resin, the ability of the resin to relax the stress is reduced, and bonds to the solder bumps may break. Also, protection from water content and moisture from the outside will be insufficient.
The purpose of the present invention is to solve the aforementioned problems of the prior art by providing a semiconductor device manufacturing method that can suppress the formation of voids in the underfill resin, so that a highly reliable flip-chip assembly can be realized.